title: Choosing the unit of measurement counts: the use of oral morphine equivalents in studies of opioid consumption is a useful addition to defined daily doses.
abstract: OBJECTIVE
  Defined daily dose (DDD) is the most common measurement unit used in drug consumption studies. The DDD for opioids may not reflect their relative clinical potencies. The aim of this study was to explore whether opioid consumption data may be interpreted differently when adding oral morphine equivalent (OMEQ) dose as a measurement unit compared with using DDD.
  
  
  METHODS
  The equianalgesic ratio of each opioid relative to morphine was tabulated. Data on opioid consumption expressed in DDD were converted to OMEQs using the equianalgesic ratios. The opioid consumption was compared in three different study settings: clinical data from an opioid switching study, trends within one country and a comparison between countries.
  
  
  RESULTS
  Using DDD, the opioid consumption in Norway between 2004-2008 increased of 6.7%, while the increase was 23.6% using OMEQ. While DDD/1000 inhabitants/day showed that Sweden had the highest consumption of opioids among the Nordic countries, OMEQ/1000 inhabitants/day showed that Denmark had the highest consumption. In the switching study DDD indicated a reduction in analgesic dosing and OMEQ an increase when switching from WHO step II to III.
  
  
  CONCLUSIONS
  OMEQ reflects clinical dosing better than DDD, and can give additional insight into opioid consumption when combined with DDD. Using OMEQ can also lead to different conclusions in opioid consumption studies compared with using DDD alone.
authors.affiliation: Department of Pain and Complex Disorders, St. Olav University Hospital, Trondheim, Norway. kristian.svendsen@ntnu.no
authors.forename: K
authors.initials: K
authors.lastname: Svendsen
authors.forename: Pc
authors.initials: P
authors.lastname: Borchgrevink
authors.forename: O
authors.initials: O
authors.lastname: Fredheim
authors.forename: K
authors.initials: K
authors.lastname: Hamunen
authors.forename: A
authors.initials: A
authors.lastname: Mellbye
authors.forename: O
authors.initials: O
authors.lastname: Dale
mesh_terms: D000284:Administration, Oral; D000701:Analgesics, Opioid / Q000008:administration & dosage / Q000493:pharmacokinetics* / Q000627:therapeutic use; D003299:Cooperative Behavior; D016208:Databases, Factual; D004363:Drug Utilization; D005283:Fentanyl / Q000008:administration & dosage / Q000493:pharmacokinetics* / Q000627:therapeutic use; D006801:Humans; D008691:Methadone / Q000008:administration & dosage / Q000493:pharmacokinetics* / Q000627:therapeutic use; D009020:Morphine / Q000008:administration & dosage / Q000493:pharmacokinetics* / Q000627:therapeutic use; D009664:Norway; D010146:Pain / Q000188:drug therapy*; D010147:Pain Measurement; D013810:Therapeutic Equivalency; D014944:World Health Organization
chemical_list: D000701:Analgesics, Opioid; D009020:Morphine; D008691:Methadone; D005283:Fentanyl